<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>
<style>
    .box {
        font-size: 18px;
    }
    
    .box1 {
        font-size: 2em;
    }
</style>

<body>

    <div class="box">
        <div class="box1"></div>
    </div>

</body>

</html>